Fibromyalgia is a common disorder characterized by widespread musculoskeletal pain, stiffness, paraesthesia, non-restorative sleep, and fatigue along with multiple tender points, which are widely and symmetrically distributed [1]. FM is an important cause of disability and work absenteeism and has major personal, social, and economic consequences [2, 3]. It affects at least 2% of the general population in the United States [4] and a similar prevalence exist worldwide [5]. It is also common in Bangladesh with a point prevalence of 4.4% [6]. Approximately 6-10% of all individuals in a physician’s waiting room have FM [7], so most physicians can expect to encounter at least one patient with FM daily.

There are several instruments available to measure the health status and physical function of patients with rheumatic diseases in general, including the Health Assessment Questionnaire (HAQ) [8] and the Arthritis Impact Measurement Scales (AIMS) [9]. Because these questionnaires do not fully reflect the multidimensionality of FM symptoms, the Fibromyalgia Impact Questionnaire (FIQ) was developed to specifically capture the total spectrum of problems related to FM [10, 11]. Since its introduction in 1991 [10], the FIQ has become a widely used and popular instrument in FM research. The scale has been translated and validated in several languages, including Hebrew, Swedish, Korean, German, French, Spanish, Italian, Turkish, and Dutch [12–21]. Overall, it has shown credible construct validity, adequate reliability, and excellent responsiveness to change and has been recommended as a primary endpoint in FM clinical trials [11, 22].

To date, however, the FIQ has not been translated into Bengali. With nearly 300 million speakers, Bengali is the sixth language in the world, second in India and the national language in Bangladesh [23]. Therefore, the aim of the present study was to cross-culturally adapt the FIQ into Bengali and to evaluate its reliability and construct validity in Bangladeshi patients with fibromyalgia.

The original US modified version of the FIQ consists of 10 items [11]. The first item contains 11 sub-items measuring the ability to perform activities of daily living in the past week on a 4-point Likert-type scale from 0 (always) to 3 (never) and is referred to as the physical function subscale. Item 2 and 3 ask for the number of days felt good and the number of days (0–7) unable to work during the past week. Items 4–10 are horizontal linear scales marked in 10 increments on which the patient rates work difficulty, pain, fatigue, morning tiredness, stiffness, anxiety, and depression in the past week. Scores on each of the 10 items are standardized so as to range from 0 to 10, with higher scores indicating greater impairment. The total score can range from 0 to 100.

Tools for evaluating health status have been developed mainly for use in English-speaking countries [29, 30]. In order to assess the health status of different cultural groups and to compare the results of trials in different countries, the need for non-English language measures has increased [31]. To date, no validated disease-specific measure was available to assess the full spectrum of FM problems in Bengali patients. In this study, we developed and evaluated a cross-culturally adapted version of the FIQ for use in Bengali-speaking patients with FM. Overall, the findings suggest that the B-FIQ is a sufficiently reliable and valid measure of health status in Bangladeshi women with FM. However, some limitations were apparent that need further study, including the low correlation between the physical function scale and similar or conceptually related scales and the low test-retest reliability of the anxiety and morning tiredness items.

Cross-cultural adaption of a questionnaire is more challenging than merely translating its items into another language. To be used across cultures, the items must not only be translated well linguistically, but also have to be adapted to the specific culture to maintain content validity at a conceptual level [24]. This may involve changing or replacing items that are not experienced in the target culture [24, 31]. To adapt the FIQ for use in Bengali patients, five sub-items of the final B-FIQ physical function scale (i.e., do laundry with a washer and dryer, vacuum a rug, walk several blocks, do yard work, and drive a car) were replaced with culturally appropriate equivalent activities since these activities are not commonly performed or understood by Bengali women. Similar modifications have been made to these items in previous cultural adaptations of the FIQ [12, 14, 21]. Additionally, several other physical function items were slightly modified or clarified. The finding that especially the sub-items of the physical function subscale needed adaptations corresponds with findings from several translations of the widely used SF-36 health status measure, which also showed that the most difficult items to translate were physical functioning items that refer to activities not common outside the US [31]. In 2009, Bennett et al. [32] developed a revised version (the FIQR) in response to several deficiencies, including the fact that the functional questions were originally intended for women living in reasonably affluent countries. It is likely that the new physical function items of the FIQR are more appropriate to Bengali women as well and could provide better cross-cultural compatibility. Therefore, it would be worthwhile for future studies to validate the FIQR in Bangladeshi patients with FM.

During the pre-testing phase, it became clear that most Bengali FM patients were not able to complete the questionnaire by themselves. Although the FIQ was developed as a self-administered questionnaire, we decided to administer the questionnaire in a face-to-face interview context. This inability to self-complete the questionnaire was most likely due to patients’ lack of previous experience with research and participation in such studies. Most patients were not familiar with completing questionnaires and scoring VASs. Also, the low literacy rate among Bangladeshi women may have contributed.

Additionally, there was a notable difference in the time it took to administer the B-FIQ to the FM patients and the healthy controls in the psychometric evaluation study. The longer administration time in the FM patients may be the result of more cognitive dysfunction in this group, which is increasingly recognized as a key symptom of FM [33, 34].

The internal consistencies of the physical function scale and the total B-FIQ were adequate for group level comparisons and suggest that scores on the sub-items of the physical function scale and the scores on all 10 items of the B-FIQ can be summed to create single total scores. With a Cronbach’s α of 0.83, the internal consistency of the total scale was comparable with previous translations of the FIQ, where α’s have ranged between 0.72 and 0.93 [13, 15, 17–19, 21]. Internal consistency of the physical functioning scale (α = 0.73) was somewhat lower than the values of 0.86 and 0.91 found in previous studies [17, 20]. Since one item was removed from the pre-final B-FIQ due to its low item-total correlation, the final B-FIQ consists of 11 items similar which are similar in content to the original US version.

The significant correlations between most FIQ items and other outcome measures suggest that the FIQ has adequate construct validity. Most notable exceptions were physical function, which only correlated with tiredness and the TPC, and workdays missed, which only correlated with the TPC. Additional analyses using selected scales from the HAQ and SF-36 as convergent measures showed that both were significantly, but only weakly, related to the HAQ disability index and the SF-36 vitality scale.

The finding that workdays missed does not correlate well with many other outcomes was also apparent in previous translation studies [14, 17, 20, 21]. This difference with the original US questionnaire may be the result of cultural differences in employment and working conditions between countries. In their evaluation study of the Dutch FIQ, for instance, Zijlstra et al. [20] argued that the low correlations were probably due to the small number of women who had a job. In the Bengali socio-cultural situation, in particular, women often cannot skip work, especially housework, even if they feel very sick. The non-significant or weak correlations between the physical functioning scale and most other measures does not correspond with most previous studies. Although in the Korean version of the FIQ this item also correlated poorly with current FM symptoms [21], most studies did find moderate to high correlations with concurrent measures such as the HAQ and the SF-36 physical functioning scale [13–15, 17, 20, 21].

Except for stiffness, all B-FIQ items were significantly but only weakly or moderately correlated with the TPC. This is in accordance with previous studies that also showed weak [10, 16, 17, 21] or moderate [13, 15, 18, 19] correlations between FIQ items and TPCs. It is also in line with findings by Jacobs et al. [35], who found a weak correlation between TPCs and self-reported pain. They concluded that TPCs and self-reported pain represent different aspects of pain in FM. Callahan and Pincus even suggested that this is a specific feature of FM [36].

The B-FIQ was highly capable of discriminating between FM patients and healthy controls and between FM patients and RA patients. Score differences between FM patients and RA patients were significant for all items except workdays missed. This is consistent with the findings by Hedin et al. in Sweden [14]. FM patients also scored worse on the number of days felt good, suggesting that the FIQ may be a more appropriate instrument for evaluating FM patients than the HAQ or AIMS.

Finally, test-retest reliability was adequate for all B-FIQ items except morning tiredness and anxiety. Low test-retest coefficients have been previously reported for morning tiredness [17, 20, 21], but not for anxiety. Other studies, however, did report low reliably for varying items of the FIQ [12, 14, 16]. Perrot et al. [16] have suggested that this may be due to the variability of the multiple aspects of the FM syndrome.

The results of this study suggest that the B-FIQ is a reliable and valid measure of health status for female FM patients in Bangladesh. Future studies should further examine the issues related to the construct validity of the physical function subscale and the reliability of the anxiety item. Additionally, the responsiveness of the B-FIQ should be examined in longitudinal clinical trials.